US2394111A - Control system - Google Patents

Description

Feb. 5, 1946. w. SCH AELCHLIN ETAL 2,394,111

CONTROL SYSTEMS Filed Sept. 28, 1944 WITNESSES; INVENTORS WQ fer5chae/chh'n 8 5F 0 0 Ear/B fiornbarye ATTORN EY Patented Feb. 5, 1946 Walter Sohaelchlin, Pittsburgh, and Earl 11.

Hornbarger, Edgewood, Pa... assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 28, 1944, Serial No. 558,160

6 Claims.

This invention relates, generally, to an electric drive and, more particularly, to an electric drive embodying an electric motor and which includes means for reversing the direction of rotation of the motor.

In certain applications of reversible electric drives space limitations are such that standard reversing equipment will not fit into the allowed space. It is also frequently required that the motor be entirely disconnected from the line when the system is stopped. Ordinarily in a reversible electric drive in which the motor is to be disconnected from the line at a minimum there is required one main line contactor and a pair of twopole mechanically interlocked contactors for reversing the connections to the motor armature.

A compact design is obtainable by utilizing, in place of the reversing'contactors, an electromagnetically operated switch which is maintained in either of its two operative positions with the actuating coils thereof deenergized. Such a re-v versing controller differs from conventional arrangements in that the reversing elements are always in one or the other of the two operating positions. In other words, the controller is always positioned for either forward or reverse operation of the motor and the motor will start as soon as a the line contactor closes. Thus suitable provision should be made to prevent closing of the main line contactor until the reversing switch or controller is in the desired position.

A principal object of this invention is to provide a reversible electric drive which is inherently compact in design and simple in operation. Another object of this invention is to provide a reversible electric drive which utilizes a simple reversing switch operable to either of its two positions, in which the reversing switch automatically assumes its correct forward or reverse position before the motor i connected to the line.

Another object of this invention is to provide a reversible electric drive in which low voltage protection is provided.

Another object of this invention isto provide a reversible electric drive in which. the reversing switch or controller is operated only to effect reversing of the direction of rotation of the motor and is not energized and therefore does not function during starting of the motor in the same direction as last operated.

Another object of this invention is to provide an electric drive of the character mentioned in which the motor must be deenergized before a reversing cycle can be initiated.

Other objects and advantages will become anparent from a study of the following disclosure when considered in conjunction with the accompanying drawing, in which the single figure thereof illustrates a reversible electric drive embodying the principles of this invention.

Referring now to the drawing, the reversibleelectric drive therein illustrated comprises generally a direct-current motor M which is reversely operable, a. reversing switch generally designated RS for establishing reversing connections for the motor armature, forward and reversing push buttons respectively designated FWD and REV which selectively energize the forward and reversing solenoids F and R of the reversing switch, an accelerating relay designated A which controls the starting cycle of the motor M and in addition initiates an energizing circuit for the coil of the main line contactor, which contactor is designated MC, and as the final general con troi element the main line contactor MC which establishes energizing circuits for the motor.

The motor M, as illustrated, comprises a pair of field windings, one a shunt field winding designated SHF and the other a series iield winding designated SRF. While two field winding have been shown for this motor it will, of course, be understood that any suitable field winding arrangement may be utilized. For example, the motor may be a series motor or a shunt motor depending upon the operating characteristics which are desired. The armature winding of the motor M is connected through either the forward or reversing elements of the reversing switch and the contacts MCI and M03, across the energizing buses BI and B2. When the reversing switch is in the position indicated in the drawing, that is the forward position, the contact members F3 and F4, thereof establish connections to energize the motor armature in a direction with respect to the motor field system such that the motor will operate in a forward direction. The contact members F2 operate in conjunction with the front contacts of the forward push button and the back contacts M04 to connect the coil of the accelerating relay A across the main line buses. The contact members Fl, when closed, provide an energizing circuit for the coil of the forward solenoid, in conjunction with the contacts API of the anti-plugging relay AP and the contacts M02 when the forward push button is depressed, to effect operation of the reversing switch to its forward position. This circuit may not be completed if a voltage appears across the motor armature terminals of sumcient magnitude to operatimz the anti-plugging rela The contacts M02.

when the main line contactor is operated, also open this energizing circuit. For reverse operation of the motor the contact members RI and R4 reversely energize the motor armature and thus cause the motor to operate in the reverse direction. The contact members R2, when closed, like the contact members F2, form part of an energizing circuit for the coil or the accelerating relay A. The contact members RI form part of an energizing circuit for the coil or the reversing solenoid R.

The accelerating relay A controls the starting cycle of the motor at'its contact members Al which shunt the starting resistor SR. This relay picks up once the reversing switch is in its correct position and opens theshunt circuit around the starting resistor at its contacts Al. Thus when the motor accelerates irom zero speed, the starting resistor is connected in series with the armature winding and the series field circuit to thus limit the armature currents within permissible values. This is desirable in the case of a.

motor which is permanently connected to the a load which it drives since under this condition the motor armature currents at very low speeds and high torque may be excessively high. The accelerating relay at its contact members A2 also forms part of an energizing circuit for the coil of the main line contactor. Thus this contactor may not be closed to energize the motor until the accelerating relay has operated. Likewise, the accelerating relay may not be operated, as hereinbeiore noted, until the reversing switch is in its correct position depending upon which of the forward and reverse push buttons is depressed.

The main line contactor at its contacts MCI and M63 energizes the motor circuits. Its contact members M62 open the energizing circuit for the coils of the forward and reverse solenoids which comprise part of the reversing switch. The Contact members M64 open the energizing circuit for the accelerating relay thus causing it to drop out shortly after the main line contector operates. Thus the resistor SR is inserted in the motor circuit for a short interval Just sufficient to bring the motor from zero speed up to some higher speed, and then is shunted to permit the motor to accelerate over the rest of its speed range. The contact members M05 in conjunction with the stop push button, so designated in the drawing, form an energizing circuit for the coil of the main line contactor to keep this coil energized when the contact members A? open.

Th operation of the system is as follows. If it is desired. to operate the motor in a forward direction, the forward push button is depressed. This establishes an energizing circuit for the coil of the accelerating relay since the reversing switch is in its forward position, which begins at the bus Bi and includes the stop push button, the back contacts of the reversing push button, the front contacts of the forward push button, the contact members F2 now closed, the coil of the accelerating relay and the contact members MC4 to the bus B2. This accelerating relay thus picks up and opens its contact members Al to insert the starting resistor in the motor circuit and closes its contact members A2 to complete an energizing circuit for the coil of the main line contactor which includes the stop push button, the back contacts of the reversing push button, the front contacts of the forward push button, the contacts F2, the contacts A2 and the coil of the main line contactor to the bus B2.

The main line contactor immediately picks up. closing its contact members MCI and MCI and immediately starts the motor in the forward direction. At this time the contacts M04 open and deenergize the coil of the relay A. This relay now drops out and shunts the starting resistor from the motor circuit. The contact members MCB close before the relay A drops out and maintain the coil of the main line contactor energized. Since the contact members MCZ have opened, the energizing circuit for the coil of the reverse solenoid is opened at this point. This actuation of the reversing push button may not complete an energizing circuit for the reverse coil. After the motor armature voltage builds up the anti-plugging relay AP is operated, thus opening its contact members API also in the energizing circuit for the forward and reverse solenoids. 'By reason of these expedients the motor may not be suddenly reversed in its direction of operation by operation of either the forward or reverse push button. To accomplish reversing of the motor it is necessary to press the stop button and deenergize the main line contactor. When the main line contactor is deenergized its contact members MC2 close. If these contacts alone maintained the energizing circuit for the forward and reversing solenoids open, it would be possible immediately upon deenergization oi the main line contactor to initiate a reversing cycle or the motor. This is prevented, however, by the antiplugging relay which will not drop out until the motor armature terminal voltage has decreased to a fairly low level, at which level a reversing cycle may be initiated without damage to the motor.

I! it had been desired to start the motor in the reverse direction with the reversing switch in the forward position, the reversing push button would have been depressed, immediately energizing the coil or the reversing solenoid in a circuit through the stop push button and the forward and reverse push buttons which includes, the contacts RI, AP! and M02. The magnetic forces acting on the core of the reversing solenoid accelerate the reversing switch to the right. This immediately opens the contacts Rl to deenergize the coil R. The assembly, however, by reason oi its inertia, moves to its extreme reverse position and closes the contacts R2, R3 and R4. The contacts R2 energize the coil of the accelerating relay A and the contacts R3 and R4 establish reversed armature connections for the motor to operate the motor in its reverse direction. The main line contactor now closes to start the motor and deenergize the accelerating relay.

Since the reversing switch operates only during periods when the motor circuits are deenergized its contacts do not interrupt energized circuits. This relay may therefore be of fairly small capacity, thus lending itself to small physical design. Further, the coils of the reversing solenoids are only intermittently energized and are deenergized by contacts within the reversing switch itself. The coils may thus be intermittently rated. In controllers which would be reversed very infrequently the reversing switch illustrated in the drawing would receive correspondingly infrequent operation. In the case of contactor-type reversing controllers the reversing devices would open and close every time the motor was started.

The reversing switch, as illustrated in the drawing, is schematically shown for the sake of simplicity and it should be understood that any asaaui physical arrangementoi' parts for this switch which embody the principles illustrated may be motor, acontactor forenergisingthe motor, a

relayhavingapairofcoilsforactuatingsaidrelay to either ortwo positions depending upon which coil is energized, means for selectively energinngsaidpairofooimsaidrelaybeingeifectiveineaehofitstwopositionstoeifectreversthereof under influence of said energized coil.

2. In an electric drive, the combination of, a motonmeans for energizing the motor, reverstionthereoi'to eitherof two positionsupon separate encrgization thereof, means for selectively energizing said pair of coils, a relay for energizing the contactor, means forming a part of said switch for energizing said relay when said switch isinthepositionselectedbysaidmeansforselectively energizing said coils; means forming a part of said contactor for deenergizing' said relay 1o vwhen said contactor is energized and operated,

a resistor connected ineseries with said motor,

andmeansformingapartoisaidrelaynormally shuntingsaidresistorwhensaidrelayisdeenergized 5. In an electric drive, the combination of, a motor, a contactor for the motor, a

switch having a pair of coils tor effecting operation thereof to either of two positions upon separate energization thereof, means for selectively energizing said pair of cells, a relay for energizln the contactor, means i'orminga part of said switch i'or energizing said relay when said switch isinthepositionselectedbysaidmeansforselectively energizing said coils, means forming a part of said contactor for deenergizing said relay when said contactor is energized and operated, a resistor connected in series with said motor, means forming a part of said relay normally shuntingsaidresistorwhensaidrelayisdeen ergiaed,andmeans for preventing tion of "eitherofsaidpairofcoilsaslong-assaidmotoris energized. v

8. In an electric drive, the combination of, a

motor, a contactor for the motor, a

switchhavingapairofcoilsforeilectingop'erationthereoftoeitheroftwopositionsuponseparate energization thereof, means for selectively energizingsaidpairofcoils,arelayfor energizlnsthecontactonmeansformingapartofsaid switchforenergizingsaidrelaywhensaidswitch isinthepositionselectedbysaidmeansforsr -lectivelyenergizingsaidcoils,meansforminga partofsaidcontactorfordsaidrelay' when said contactor is energized and operated, a resistor connected in series with said motor,

meansformingapu'tofsaidrelaynormaily .shuntingsaidresistorwhen saidrelayis deenergined,andareiayaccordingtothe motor voltage and having contacts which maintaintheenergizingcircuitsforsaidpairofeoils' openaslongasthemotorvoltsgeisabovea determinedvalue. v s

"WALTER SCHAEICHLIN.

EARLEHORNBARGER

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